Observations on the Song Thrush Turdus philomelos Brehm at Shadwell Wood SSSI
as a major part of their diet (Simms op. cit.). In dry years, as the water table falls, worms move lower
into the ground and are harder to find for surface feeding animals. Wet boulder clay woodlands such
as Shadwell Wood retain their soil moisture much longer than the surrounding arable land or gardens;
hence worms are easier to find here in the drier times of year. This may explain an increase in numbers
of thrushes in dry years. In a landscape in which there is less woodland cover and individuals cannot
change habitats one might predict the drier years to have an ad verse impact on thrush numbers. Although
there was no correlation between thrush numbers in any year and the previous year's rainfall, recent
work by Peach et al. (2004) suggests that lack of food, such as fewer worms in dry conditions, reduces
nesting attempts by thrushes. This effect is more noticeable in the arable environment.
Although thrushes have been reported feeding and singing in all parts of the woodland structure from
the ground layer to high canopy, the evidence suggests that they prefer low canopy and scrub layers
(Simms op. cit.). Simms suggests they favour shrubs between 7 and 14 years old. The results in
Shadwell Wood would support this, with far more contacts being made in the coppiced areas of the
wood than in the mature non-intervention areas. A number of reasons may be put forward for this.
Firstly the dense structure of young coppice offers more warmth and security when nesting and raising
young. Secondly coppice areas will have a higher invertebrate population in the summer when young
birds are being fed. Lastly coppiced areas will generally have more vegetable matter for autumn feed
particularly in the form of berries, although this would appear to not be the case here.
Blackbirds are probably the Song Thrush's closest competitors for food and habitat, and this is
very evident in our gardens where the Blackbird is considerably more numerous. In Shadwell
Wood this is much less evident, however. Those years in which the Blackbird does particularly
well do not result in a decline in Song Thrush numbers in either the same or subsequent years.
The contacts show7 that although the two species overlap in their use of habitat within the wood,
Blackbirds favour the non-intervention woodland more than the coppice. This is the opposite of
the Song Thrush, and probably reduces direct competition for nesting sites and perhaps food
sources. The lack of any correlation between Song Thrush and Blackbird numbers may suggest
that the factors affecting their numbers are not the same.
Possible lessons for Song Thrush conservation
This work did not identify a population problem for the Song Thrush in Shadwell Wood during
the trial period. It does perhaps, however, suggest some factors that might help to encourage the
species.
• Maintaining the coppicing cycle will provide the favoured habitat for the species within
woodland
• Retaining a diverse age structure within the same wood may help to reduce the direct
competition between Blackbirds and Song Thrushes.
• Encouraging the thrushes favourite autumn food sources may help to entice them into the
wood at this time of year. Hawthorn would be the main species that would not conflict with
other conservation objectives and would also attract more invertebrates in the summer when
thrushes need them most.
• Maintaining the dampness of the wood, whilst essential for the flora, may help the thrushes
food supply in dry years.
• Increasing the proportion of scrub and grassland in the arabic environment will favour
thrush populations.
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Essex Naturalist (New Series) 21 (2004)